The improver of natural knowledge absolutely refuses to acknowledge authority, as such. For him, skepticism is the highest of duties; blind faith the one unpardonable sin. Thomas Huxley

Thursday, May 23, 2013

A Tale of Two Scrapers

A follow-up piece - how Did I manage to Break a Scraper in Half?

First up, I was working for the Copulating Spiders - the ol' MoW insignia. The gear was probably 20+ years old (in 1972-3), and instead of a proper Cat tow-pin between dozer and scraper, MoW being the cheapskates they always were, had thoughtfully supplied a shortened piece of truck axle. Didn't quite fit the hole - rattled around a bit.

A fully loaded scraper could hold around 15-20 cubic metres of spoil (roughly a 3x3 floor pan, and could be crowded in good stiff clay to 3+ metres high) so I guess total weight could run 35-45 tons all up. A twin-drum winch on the dozer needed for the two operation cables: one for blade height, one for apron trim and material eject/spread. Dozer was a 3T series Caterpillar D7 - see one at work here.

The usual round (this was topsoil stripping, to a temporary heap) was

run the dozer in high gear to the pickup,

change (on the fly, yes, possible) to low,

drop the blade into the material,

let the material crowd (if it would) until it spilled over,

raise the pan to travel position,

crawl back to the heap and up it,

wind the dump winch which first raised up the front apron and let the material out, and then pushed the whole rear wall of the scraper forward, ejecting all material.

Bring 'er back to travel mode, high gear, off the heap,

wash, rinse, repeat. 50-100 times per day - an average round was perhaps 3-5 minutes.

Working this gear gets quite repetitive, so the old mind tended to wander.

So it was, coming off the heap in high gear, with quite some surprise that I was awakened from my reverie to hear both winches screaming their heads off. Turned around to ascertain the cause.

Oh dear.

The tow-pin had sheared. The scraper was in two pieces, quite a few metres back from the accustomed position. The cables were running out against the brakes, hence the screams.

The scraper, empty but running down a 20-degree slope, had promptly dug in the towbar to the ruffled surface of Gaia, run clean over it tilting it around 180 degrees so it ended up facing backwards, and comprehensively foobarred the ball joint that joined the front set of wheels plus towbar, to the rest of the scraper. Not a good look. A two-piece scraper. Here's a one-piece....

What to do?

Uncouple the cables from the winches (hammer and wedge), run back for the dozer blade and hook it on, string its cable onto one winch, and proceed to move the pieces out of the way of the heap.

Then confess all to the bosses, but point out that a Real Caterpillar Towpin would be henceforth a Good Idea.

We ended up (days later, this was Gummint work, y'unnerstand) going way out to the backblocks of Fortrose, and bringing back another even more ancient scraper, with which I (lopsidedly - darn thing had two different sized tyres on the back, which controls cutting attitude) completed the earthworks.

With (what joy!) a Real Caterpillar Towpin which appeared, along with the immortal words 'Let's see if you can manage to f... This one Too!'

A little addition, about Elfin Safety.

The old D7 had zero electrics: it was a hand-crank petrol pony motor start.

But the crank handle was vertical.

So, the Elfin Safety issues to start the beast:

stand, in yer gummies, on an iced-up top track, in a typical Invercargill frost.

prime the pony motor and offer up a small prayer to the appropriate deities

Insert the crank handle from on top of the bonnet (about chest height IIRC)

Pull it gently around to compression on the pony motor.

Take another purchase on the crank (no thumbs around the handle...) and mutter another smaller prayer.

Pull the crank smartly towards you.

If lucky, pony fires and runs. Trim it, engage the clutch and turn over the main donk.

If not lucky, pony backfires and pulls you straight into the edge of the bonnet (curved, fortunately).

If really not lucky, bounce off bonnet, slip on top track, clobber appendages on the way down to the cold hard ground a metre below.

If inclined to Push the crank to start, expect the backfire to merely throw you off of the track. No bonnet edge. Take yer pick.